(1) Field of the Invention
The present invention relates to a scene change detecting device for detecting the position of a frame where a scene changes in a moving picture, and more particularly to a scene change detecting device for detecting a scene change frame in a moving picture which has been processed by block-adaptive interframe predictive coding.
(2) Description of the Related Art
The recent development of multimedia technology has necessitated a new system for editing and searching for multimedia information. Particularly, it is important to edit and search for moving pictures efficiently because moving pictures contain much information among various forms of multimedia information. Editing and searching for a moving picture makes it indispensable to recognize each of the scenes which make up the moving picture. It has been customary to recognize the position of a scene change in a moving picture based on the fact that the correlation between a scene and a previous scene is greatly reduced in the first frame of the former scene.
Conventional scene change detecting processes are disclosed in Japanese laid-open patent publications Nos. 6-153146, 6-22298, and 6-259052, for example. According to these disclosed scene change detecting processes, a motion vector and discrete cosine transform (DCT) coefficients are calculated with respect to each of the pixels of a moving picture to detect a reduction in the correlation between scenes.
International standards such as ITU-T H.261, ISO/IEC MPEG-1, ISO/IEC MPEG-2, etc. are available for moving picture compressing and coding processes in order to achieve the storage and transmission of digital moving pictures which contain a vast amount of information. These moving picture compressing and coding processes process image information according to interframe predictive coding. One known apparatus for carrying out such a moving picture compressing and coding process detects a scene change as disclosed in Japanese laid-open patent publication No. 6-54315, for example. According to a disclosed scene change process, the standard deviation of image data in each 8.times.8 macroblock in a present frame is determined and compared with the standard deviation of image data of a similar macroblock in a previous frame. When the former standard deviation is smaller than the latter standard deviation, a coding mode for the macroblock in the present frame is set to an intrablock coding mode. When the former standard deviation is greater than the latter standard deviation, a coding mode for the macroblock in the present frame is set to a motion compensating mode. The number of macroblocks that enter the intrablock coding mode is counted. If the count is greater than half the number of macroblocks of one frame, then it is determined that scene change has occurred.
The scene change detecting processes disclosed in the former publications need a scene change detecting circuit which is inevitably large in scale because of calculations of a motion vector and discrete cosine transform (DCT) coefficients required with respect to each of the pixels of a moving picture.
The scene change detecting process disclosed in the latter publication requires a scene change detecting circuit smaller in scale than the scene change detecting circuit needed by the scene change detecting processes disclosed in the former publications because a scene change can be detected by monitoring a coding mode for each of the macroblocks. However, the scene change detecting circuit required by the scene change detecting process disclosed in the latter publication suffers limitations in that it functions only when information as to whether a coding mode is an intrablock coding mode or not is given from a compressing and coding device.
Inasmuch as digital moving pictures contain a very large amount of information, data which have already been compressed and coded will be provided and used more frequently for detecting scene changes. In order to operate the scene change detecting circuit required by the scene change detecting process disclosed in the latter publication, based on such data which have already been compressed and coded, it is necessary to decode those compressed and coded data. There has been a demand in the art for an apparatus capable of detecting a scene change by directly using data which have already been compressed and coded.